Closed railway hopper cars with pneumatic systems for unloading are often used for the transportation of powdered and granular products. For cars with positive pressure pneumatic systems, air is supplied from an external source to pressurize the interior of the car body and simultaneously fluidize the dry, bulk product carried within the car to enable it to be conveyed in a fluidized state in an air flow through product transfer conduits from the car. Air pressure within the hopper car during the unloading procedure may be maintained at approximately fifteen psi gage. The pneumatic discharge or unloading system associated with a pressure discharge railway hopper car may include an air supply conduit for directing a portion of the air supplied to the hopper car into the discharge line leading from the car to the destination of the product being discharged. The air pressure in the discharge line may be maintained at two or three psi below the pressure within the hopper car.
Trinity Industries, Inc., the assignee of the present invention, manufactures and sells Power Flo.RTM. pressure discharge railway cars with pneumatic unloading systems. An example of aeration equipment and a pneumatic discharge system for removing dry, bulk material from hopper style containers is described and shown in U.S. Pat. No. 3,929,261 entitled Aeration Device and Method for Assisting Discharge of Material from Containers. Reference may also be made to U.S. Pat. No. 5,433,559 entitled Pressurized Hopper Car.
Flours, starch and similar powdery food products are examples of dry, bulk material suited for loading, transportation and discharge with an enclosed hopper car having a positive pressure pneumatic unloading system. Any dry powder, granular, or pellet-form commodity may, usually to advantage, be transported in such hopper cars. An enclosed hopper car and the pneumatic discharge apparatus protect the contents of the car and minimizes product losses during the loading, transportation, and the discharge process. Also, pneumatic transport is often the most cost effective, efficient method of moving large quantities of dry, bulk product.
Pressure discharge hopper cars may have a single product outlet leading from each hopper located near the center of the car and opens to a hopper discharge conduit located therebelow. Discharge conduits connected to each hopper outlet communicate with the hopper outlet and are typically connected to a main product transfer conduit extending along the side of the car. Providing piping immediately below each hopper outlet within appropriate American Association of Railroads (AAR) plate may limit the height above the track of the bottom of each hopper.